There seem to be a lot of people running around with their hair on fire, lamenting that Iran will get nuclear weapons and Israel will become a smoking hole. The history of nuclear weapons suggests otherwise. Nuking Israel would be suicide for Iran, as Israel (and the US) would retaliate in kind. There is no reason to think that Iran is suicidal. There is no cause for fear that it would behave differently from the other nuclear countries.
The main effect of an Iranian nuclear program would be that Israel would no longer be the sole nuclear power in the middle east. This could be a good thing. Creating a more balanced power structure could actually help Israel's relations with its neighbors.
I have some concerns, and I don't know how valid they are.
One: In the past, Iran has expressed some hegemonic tendencies. Its backing of Syria's suzerainty over Lebanon is a concern. However, Iran is primarily Shia Muslim, and the only other countries where Shia is the largest religious group are Iraq, Azerbaijan, and Bahrain. Shia is a minority in Syria but the government is Shia. Does this limit Iran's sphere of influence, or sphere of interest? Is there a real interest in this Shia, non-Arab country to take over Arab, Sunni states?
Two: Iran's close relationship with North Korea. However, does Iran really want to be involved with North Korea, or has it become so isolated and threatened that it's making the only ally it can?